The present invention relates to multimedia processing. One example of multimedia processing is the processing of video, audio or combined video and audio signals to apply special effects to a single signal, or to combine two or more such signals in a specified manner, or to perform both processing and combining. For example, in a television production environment, the producer may want to distort the video from one source according to some geometric scheme, transpose portions of another video signal according to a different scheme which varies with time in some way, and combine these two processed video signals in a particular manner to form a composite output signal. It would be desirable to combine the advantage of a computer operating according to a conventional operating system, with the special-purpose media processing devices. Such device can operate, for example, according to a real-time operating system and can process multimedia data at speeds not readily achievable in a conventional multipurpose computer.